1. Field of the Invention
The present invention is directed to improvements for killing phreatophytes, especially tamarix pentandra, and for preserving ground water in arid areas infested with such plants.
2. Description of the Prior Art
In arid climates, such as the southwestern United States, useful ground water is constantly removed by large-scale infestation of phreatophytes. A particular widespread offending plant in large areas of New Mexico and Arizona is tamarix pentandra, commonly known as the salt cedar. This plant was originally introduced to this area from the Mediterranean as an exotic ornamental in the 1920s. Used for a time for erosion control, it has now grown wild and spread along the river systems of the southwestern states, notably parts of California, Arizona, New Mexico and Texas.
This phreatophyte taps ground water and by transpiration expels it into the above-ground atmosphere. Various studies have been done on the large quantity of water that such plants remove from the ground. Some of these studies are summarized in "Assorted Phreatophyte Water-Use Studies" published as "Appendix J" in the appendix to "Final Environmental Impact Statement Operation and Maintenance Program for the Rio-Grande--Velarde to Caballo Dam, Rio Grande and Middle Rio Grande Projects", U.S. Department of the Interior Bureau of Reclamation.
An early survey of the problem caused by this and like plants occurred during the hearings of the Senate Select Committee on Water Problems in 1958, and since then numerous studies and attempts at amelioration of the problem have been undertaken, primarily by the use of herbicides, burning and ploughing.
Herbicides pose hazards both obvious and subtle, not only to mankind directly, but also to the ecology on which all life depends. The chief objection of the water conservation people is that herbicides are spread from crop-dusting planes and tend to drift over onto adjoining ranch and farm land, engendering lawsuits. Also, certain long-lived herbicides tend to be washed into the ground water by the occasional rains in the areas and harm the very water that the users are attempting to preserve.
Burning, unfortunately, does not usually work. The wood tissue of the plant is so permeated with water and carbon dioxide that it must be sprayed with oil before it will burn. This procedure is relatively expensive, but even so, only a very occasional individual plant of exactly the right characteristics will succumb. Most burnt plants will put up new growth in the following year and in four or five years will have regained original size.
The only consistently reliable prior art method or eradication is ploughing, but as the salt cedar has a decided affinity for swampy, soggy locations, it is not physically possible to reach a high percentage of the plant population with heavy equipment. The giant ploughs necessary to do this work are very expensive and the work itself is rough on the equipment.